Investigation of the toxic effects of the prominent air pollutants, ozone (O3) and sulfur dioxide (SO2), on the respiratory tracts of amphibians will be continued. Inhaling exposure studies of these representative upper airway (S02) and low airway (O3) irritants will be performed in our model amphibian and reptile species, the marine toad (Bufo marinus) and house gecko (Hemidactylus frenatus). In addition to our earliest analyses of effects on thermoregulation, breathing pattern, gas exchange, and pulmonary macrophage phagocytosis capacity, we will explore new potential biological effects. We will determine respiratory tract tissues that are the targets of airway irritants using analyses of epithelial cell proliferation and measures of reactive oxygen species in tissues including the airways, lung, and, for the cutaneous respiring amphibian, the skin. Investigation of the compromise of immune function by toxic exposure will be expanded with an analysis of the thermal dependence of macrophage phagocytosis capacity and the impact of pollutant exposure on that dependence. We will also measure pollutant effects on the respiratory burst capacity of pulmonary macrophages. Exercise performance measures will be developed in the model animals and used to test the effects of exposure and the statistical relationships of individual variation in performance and inhalation sensitivity. With an established batter of analytical evaluations for toxic exposure, we will then test whether animals in the field show detectable acclimatization response to natural SO2 exposure from volcanic emissions of the Island of Hawaii. These experiments will provide range-finding assays of the toxic effects of air pollution that may be important in conservation of wild populations of amphibians and reptiles, and we may discover new useful models for inhalation toxicology.